In recent years, server virtualization that utilizes a virtualization technology is widely used. By utilizing a virtualization technology, the costs related to constructing and operating an infrastructure can be reduced since physical resources such as CPU (Central Processing Unit) and memory can be effectively utilized.
As a service that utilizes a virtualization technology, there is the VPS (Virtual Private Server) hosting service that rents virtual servers instead of physical servers. Compared to a rental service of physical servers, the VPS hosting service can provide services at low rates by utilizing the cost reduction effect due to virtualization.
When there is no load, the resources to be used can be further reduced by temporarily suspending the virtual server. For instance, in a case where the virtual server is a Web server, a state without any load is one in which there is no HTTP (Hypertext Transfer Protocol) communication to the virtual server. When the virtual server is suspended, the memory used by the virtual server is released after its contents are written to a disk. Further, the virtual server stops consuming the CPU resources. Therefore, temporarily suspending the virtual server increases the physical resources available to a physical server that has been running the virtual server. Further, increasing the number of virtual servers suspended reduces the number of physical servers needed to operate a system and it becomes possible to reduce costs required for bringing in and operating the system.
As a related technology, Patent Literature (PTL) 1 describes a technology that freezes a job being executed by giving a freezing instruction to a virtual server executing the job and that has the virtual server resume executing the frozen job by giving a resume instruction to the frozen virtual server. Further, Patent Literature 2 describes a technology that realizes migration of a virtual machine (virtual server) based on OpenFlow (refer to Non Patent Literatures (NPLs) 1 and 2).    PTL 1:    WO2007/108062A1    PTL 2:    Japanese Patent Kokai Publication No. JP2011-070549A    NPL 1:    N. McKeown, et al., “OpenFlow: Enabling Innovation in Campus Networks,” Mar. 14, 2008, [online], [searched on May 21, 2012], the Internet, <URL:http://www.openflow.org/documents/openflow-wp-latest.pdf>.    NPL 2:    “OpenFlow Switch Specification, Version 1.1.0 Implemented (Wire Protocol 0×02),” Feb. 28, 2011, [online], [searched on May 21, 2012], the Internet, <URL:http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf>.